ASSEMBLY OF AN INFORMATION BEARING POLYMER:

1. ASSEMBLY OF AN INFORMATION BEARING POLYMER: • PROTEINS FIRST? • Strong points: • Easy to synthesize amino acids under a variety of conditions and polymers can also be formed. • Even small peptides can exhibit catalytic activity. • 20 amino acids provides for high information content. • Weak points: • Globular structure and lack of complementarity preclude self-replication. • Modern proteins can not function without DNA.

2. ASSEMBLY OF AN INFORMATION BEARING POLYMER: • AN RNA WORLD? • Strong points: • RNA has some catalytic properties (self-splicing introns). • RNA is capable of making proteins (Noller 1992). • Weak points: • RNA lacks the ability to self-replicate. A DNA WORLD? • DNA is almost completely lacking in catalytic ability

4. The HOLY GRAIL of Origin-of-Life Research: • Discovery of molecular system capable of SELF-REPLICATION and of carrying INFORMATIONAL CONTENT.

6. EVOLUTION OF EARLY LIFE FORMS

7. CURRENT TIME EXTINCT LINEAGES COMMON ANCESTOR OF ALL LIFE ON EARTH “CENANCESTOR” ORIGIN OF “LIFE” ORIGIN OF EARTH

8. If the theory (of evolution) be true it is indisputable that before the Cambrian stratum was deposited long periods elapsed…and that during these vast periods the world swarmed with living creatures… (However), to the question why we do not find rich fossiliferous deposits belonging to these earliest periods…I can give no satisfactory answer. The case at present must remain inexplicable…. Charles Darwin 1859

9. RECONSTRUCTING “LUCA” Last Universal Common Ancestor • The properties of LUCA have been difficult to reconstruct given the extremely long time periods involved. • Whole genome sequences of diverse prokaryotic lineages reveal ~60 “universal genes”. Far short of the ~600 genes it is estimated are required for a minimal set in a functioning organism. • Extensive gene shuffling through horizontal transfer may make it impossible to deduce the properties of “LUCA”. • Hyperthermophiles seem to at the base of the phylogenetic tree.

10. Number of Predicted Genes from 244 complete bacterial and archaeal genomes Smallest free living organism Giovannoni et al. 2005 Science 309:1242-1245

11. CAPTURE OF ORGANELLE GENOMES

12. Ancient prokaryotes from Western Australia. Filamentous “Cyanobacteria” 3.5 BYA

13. Earliest filamentous microfossils 3.23 BYA FROM: Rasmussen 2000 NATURE

14. Microfossil Cyanobacteria

15. Stromatolites from Western Australia:

16. THE ORIGIN OF EUKARYOTES • EARLIEST PROBABLE EUKARYOTES ARE SINGLE-CELLED ALGAE FROM 1.6 BYA.(Although some researchers suggest there is evidence as old as 2 BYA) • Definitive evidence for eukaryotes exists from about 1.2 BYA in the form of fossils of multi-cellular algae. Red algae fossil; 1.2 bya

17. EUKARYOTE PROKARYOTE

18. ENDOSYMBIOTIC ORIGIN OF EUKARYOTES?

19. ORIGIN OF ORGANELLES MITOCHONDRIA RICKETTSIA CHLOROPLAST

20. Requisite steps include a lateral gene transfer from the symbiont to the host nucleus and the establishment of protein transport machinery back into the symbiont, resulting in loss of the symbiont_s autonomy (2). Synchronization of host-symbiont cell cycles and cosegregation is another critical step in permanent fusion of the two partners. However, how the synchronization occurs and how the integrated organism responds to external conditions are unknown. A Secondary Symbiosis in Progress? Noriko Okamoto and Isao Inouye* Fig. 1. (A) Hatena (ventral view). All green, symbiont-possessing cells have an eyespot at the cell apex (arrowhead). Scale bar, 10 mm. (B) A dividing cell (ventral view). The symbiont is always inherited by only one of the daughter cells. Scale bar, 10 mm. (C) The ultrastructure of eyespot integration (longitudinal view). E, eyespot granules. Scale bar, 400 nm. Inset: A magnified view of the membranes. The inner and outer plastid membranes (arrowheads), the single symbiont-enveloping membrane (double arrow), and the host plasma membrane (arrow) are tightly layered. Scale bar, 50 nm. (D) The life cycle of Hatena, based on observations of natural populations. Hatena alternates between a host phase that harbors a green endosymbiont and a predator phase that acquires the endosymbiont after division. Solid line, observed steps in the process; broken line, hypothetical steps. Nature Oct 2005

21. A genomic timescale for the origin of eukaryotesS Blair Hedges1, Hsiong Chen1, Sudhir Kumar2, Daniel Y-C Wang1, Amanda S Thompson1 and Hidemi Watanabe3 BMC Evolutionary Biology 2001 1:4

22. The beginning of eukaryotic diversification dates as far back as 1.75 BYA. • Most of the diversification of the major lineages occurred prior to 750 MYA

23. EVOLUTION OF SEXUAL REPRODUCTION

24. Primitive Eukaryote: Giardia lamblia • Giardia has two haploid nuclei • No mitochondria (???)

25. EVOLUTION AND DIVERSIFICATION OF THE EUKARYOTES • What factors contributed to the rapid diversification of eukaryotic lineages? • Increased atmospheric O2 concentration – switch to aerobic respiration? • Global climate change – Major ice age around 2.7 BYA? • Evolution of sexual reproduction?

26. Divergence dates based on ribosomal RNA genes 1.2 BYA 2.8 BYA 2.7 BYA 2.7 BYA FROM: Knoll 1999 Science

27. How do early organisms fit in the tree of life? Earliest fossils: ~1.8 bya Earliest fossils: potentially 3.45 bya; abundant by ~2.6 bya, corresponding to rise in oxygen Earliest fossils: ~3.5 bya

28. CELL-CELL COMMUNICATION EVOLUTION OF SEX (Meiosis) ORIGIN OF THE NUCLEUS AND ORGANELLES ORIGIN OF LIFE Ancestral humans 0.002 Diversification of mammals Invasion of the land 0.6 Diversification of animals 1.0 Origin of the major eukaryotic groups 1.9 Eukaryotic cells abundant 2.8 Atmospheric oxygen plentiful 3.6 Simple cells abundant 3.8 Stabilization of the earth 4.6 Origin of the earth BYA